Starter for internal combustion engines

ABSTRACT

A compact starter for internal combustion engines wherein the armature shaft of an electric motor rotates an axially movable pinion through the medium of an overrunning clutch which allows the pinion to rotate relative to the shaft when the pinion meshes with a gear of the engine and the gear is rotated by the engine upon completion of the starting operation. A shifting sleeve for the pinion has steep internal threads meshing with complementary external threads of the shaft and is connected to the clutch and pinion so that the pinion moves with the sleeve toward engagement with the gear of the internal combustion engine when the sleeve is held against rotation with the shaft by a brake whose parts are mounted on and surround the sleeve. The brake operates between a flange of the sleeve and a blocking cylinder which is rotatably mounted on but normally rotates with the sleeve by way of the brake. An electromagnet is energizable in response to starting of the motor to move a pin into engagement with one of several external teeth on the blocking cylinder whereby the brake holds the sleeve against rotation and the sleeve moves axially of the rotating shaft to engage the pinion with the gear. When the electromagnet is deenergized, a return spring is free to move the sleeve axially in a direction to disengage the pinion from the gear.

United States Patent [1 1 Reichardt et al.

[451 1 Mar. 4, 1975 [75] Inventors: Wolfgang Reichardt, Sevres; Lucien Blanchard, Mitry; Jean Denamps, Asnieres, all of France [73] Assignee: Robert GmbH Bosch, Stuttgart,

Germany 22 Filed: Feb. 7, 1974 21 Appl. No.: 440,227

[30] Foreign Application Priority Data 57 1 ABSTRACT A compact starter for internal combustion engines wherein the armature shaft of an electric motor rotates an axially movable pinion through the medium of an overrunning clutch which allows the pinion to rotate relative to the shaft when the pinion meshes with a gear of the engine and the gear is rotated by the engine upon completion of the starting operation A shifting sleeve for the pinion has steep internal threads meshing with complementary external threads of the shaft and is connected to the clutch and pinion so that the pinion moves with the sleeve toward engagement with the gear of the internal combustion engine when Feb. 9, i973 Germany 2306364 the Sleeve is held against rotation with the Shaft y a brake whose parts are mounted on and surround the 52 us. Cl 74/7 R Sleeve- The brake Operates between a flange of the [51] Int. Cl. F02n 11/00 Sleeve and a blocking cylinder which is rotatably 5g w f Search H 74 7 R' 7 290 37 R, mounted on but normally rotates with the sleeve by 290/33 R way of the brake. An electromagnet is energizable in response to starting of the motor to move a pin into 5 References Cited engagement with one of several external teeth on the UNITED STATES PATENTS blocking cylinder whereby the brake holds the sleeve against rotation and the sleeve moves axially of the rotating shaft to engage the pinion with the gear. When j the electroma net is deener ized, a return spring is 2.903.892 9/1959 Buxton et al 74/7 R X ree to mo e tie sleeve axiall y n a d ection o d se Primary E.raminerAllan D. Herrmann gage the pmlon from the gear Atlorney, Agent, or Firm-Michael S. Striker 17 Claims, 2 Drawing Figures PATENTEDHAR 41915 3868 858 sum 2 95 2 Fig. 2

STARTER FOR INTERNAL COMBUSTION ENGINES CROSS-REFERENCE TO RELATED APPLICATION Certain details of the starter of the present invention are somewhat similar to the details of a starter which is disclosed in the commonly owned copending application Ser. No. 371,564 of Pfluger et al., filed June 19, 1973.

BACKGROUND OF THE INVENTION The present invention relates to improvements in starters for internal combustion engines, and more particularly to improvements in starters wherein a pinion is movable axially ofa drive shaft into and out of mesh with a gear of the engine and is driven by the shaft through the medium of an overrunning clutch.

In certain presently known starters for internal combustion engines, the means for shifting the pinion into mesh with the gear of the engine comprises an electromagnet, one or more levers, switches and/or other component parts which are mounted on and externally of the housing of the electric motor which rotates the pinion. It is also known to place the shifting means for the pinion in axial alignment with the motor shaft, for example, adjacent to the commutator. In each instance, the shifting means occupies a substantial amount of space which is particularly undesirable in recent types of automotive vehicles embodying bulky antipollution devices. In such vehicles, the space is at a premium so that there exists an urgent need for compact starters.

SUMMARY OF THE INVENTION An object of the invention is to provide a starter for internal combustion engines which is more compact than but just as reliable as presently known starters.

Another object is to provide a novel and improved mechanism for shifting the pinion of a starter into or out of mesh with a torque-receiving gear of the internal combustion engine.

A further object of the invention is to provide a shifting mechanism which is sufficiently compact to beinstalled directly in the housing of a starter without contributing to the bulk of the housing.

An additional object of the invention is to provide a shifting mechanism which can be installed in the casing of the motor and/or in the casing of the transmission of a starter for internal combustion engines.

Still another object of the invention is to provide a shifting mechanism which is particularly suited for use in starters for engines in vehicles embodying antipollution devices.

A further object of the invention is to provide a starter which embodies the improved shifting mechanism and which can be used as a superior (especially space-saving) substitute for conventional starters.

The invention is embodied in a starter for an internal combustion engine having a torque-receiving first gear. The starter comprises a motor (preferably an electric motor) having a drive shaft or armature shaft which is rotatable in a predetermined direction, operating means (e.g., a master switch) which is actuatable to start the motor, a second gear (e.g., a pinion) which is rotatably mounted on the shaft and is movable relative to the shaft axially in a first direction from a disengaged or starting first position to a second position of torquetransmitting engagement with the first gear and in a second direction back to the first position, a shifting sleeve which surrounds and can rotate with the shaft, an overrunning clutch which is mounted on the shaft between the sleeve and the second gear and serves to rotate the second gear in response to rotation of the shaft as well as to permit the second gear to rotate relative to the shaft in the predetermined direction when the second gear is driven by the first gear at a speed exceeding the speed of the shaft (i.e., when the engine is started and rotates the first gear), displacing means having portions provided on the shaft and on the sleeve for moving the sleeve axially in the first direction when the sleeve is held against rotationwith the shaft (such displacing means may comprise a steep external thread on a portion of the shaft and a complementary internal thread in the sleeve), means (e.g., a shell or casing of the overrunning clutch) for connecting the second gear and the clutch to the sleeve so that the second gear moves toward its second position in response to axial movement of the sleeve in the first direction, and means for holding the sleeve against rotation with the shaft, preferably in response to actuation of the operating means for the motor.

The means for holding the sleeve against rotation with the shaft preferably comprises a cylindrical blocking member which is rotatably. mounted on the sleeve, arresting means which is actuatable (preferably in response to actuation of the operating means for the motor) to interrupt the rotation of the blocking member, and brake means interposed between the blocking member and the sleeve. The brake means may comprise a ring-shaped coupling member which rotates with but is movable axially of the: sleeve, a first brake disk interposed between one axial end of the blocking member and the coulping member, a second brake disk interposed between a flange at one axial end of the sleeve and the other axial end of the blocking member, and means for biasing the coupling member toward the one end of the blocking member so that the coupling member urges the first brake disk against the blocking member and the latter urges the second brake disk against the flange. The means for biasing may comprise a helical spring which reacts against a retainer at the other axial end of the sleeve.

The aforementioned arresting means may comprise one or more external projections or teeth on the blocking member, a pin or an analogous arresting element which is reciprocable in the housing of the starter toward and from engagement with a tooth of the blocking member, and an electromagnet whose winding is energizable in response to starting of the motor to move the pin into engagement with an oncoming tooth of the blocking member.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved starter itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary axial sectional view of a starter which embodies the invention; and

FIG. 2 is a transverse sectional view as seen in the direction of arrows from the line IIII of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The starter of FIGS. 1 and 2 comprises an electric motor I and a transmission 2. The armature 4 of the motor 1 is mounted on a drive shaft or armature shaft 3 a portion of which is provided with steep external displacing threads, as at 5, in mesh with complementary internal displacing threads of a shifting sleeve 6. The right-hand end portion of the shaft 3 is rotatable in a bearing plate (not shown) and the left hand end portion of the shaft 3 extends into a friction bearing 7a provided in a beak-shaped extension 7 of a casing 8 forming part of the transmission 2. The externally threaded displacing portion of the drive shaft 3 extends with clearance through an aperture 9 in a plate-like abutment member 10 which is installed in the transmission casing 8. The abutment member 10 is adjacent to that end portion of the casing 8 which is in abutment with the casing 11 for the motor 1. The casings 8 and 11 together constitute a composite housing for the component parts of motor 1 and transmission 2. The means for connecting the casings 8 and 11 to each other comprises a set of through bolts 12 shown in FIG. 2.

That end portion of the internally threaded sleeve 6 which is adjacent to the armature 4 of the motor 1 carries a sleeve-like bearing member or retainer 13. The other end portion of the sleeve 6 is provided with a radially outwardly extending flange 14, and an intermediate portion of the sleeve 6 is formed with a spur gear having an annulus of axially parallel teeth or splines 15 extending into internal grooves of an axially movable ring-shaped coupling member 16 which forms part ofa brake for and shares all angular movements,of the shifting sleeve 6. A helical spring 17 which also forms part ofthe brake reacts against the left-hand end face of the retainer 13, as viewed in FIG. 1, and bears against the coupling member 16 so that the latter tends to move axially toward the extension 7. An annular lining 18 is riveted or otherwise secured to that side of the abutment member 10 which faces away from the armature 4. A helical resetting or restoring spring 19 for the sleeve 6 reacts against the other side of the abutment member 10 and bears against a flange 13a of the retainer 13; the latter shares all axial movements of th sleeve 6 or vice versa.

The brake including the components 16, 17 forms part of a device for holding the sleeve 6 against rotation with the shaft 3, and this device further comprises a blocking cylinder 20 which surrounds and is rotatable on the sleeve 6. That end portion of the blocking cylinder 20 which is nearer to the coupling member 16 of the brake is formed with a radial flange 21 having one or more axially parallel passages or recesses 22. The aforementioned brake further comprises a first brake disk 23 which is installed between the coupling member 16 and blocking cylinder 20 and has bent-over projections or prongs 24 extending into the recesses 22 of the flange 21. Thus, the brake disk 23 and the blocking cylinder 20 are rotatable as a unit. The flange 14 of the sleeve 6 is also formed with one or more axially parallel passages or recesses 25 for the bentover projections or prongs 26 of a second brake disk 27 which surrounds the sleeve 6 between the flange l4 and the blocking cylinder 20. The prongs 26 insure that the brake disk 27 cannot turn with respect to the sleeve 6.

That side of the flange 14 which faces away from the blocking cylinder 20 is formed with an annulus of five equidistant pin-shaped proturberances 28 each of which serves as a stop for one of five rollers or sprags 29 forming part of an overrunning clutch 30 of the type known as outer-wedge one-way clutch. The clutch 30 further comprises an outer race 31 which abuts against the left-hand side of the flange 14, as viewed in FIG. 1, and surrounds the rollers 29, and an inner race 32 which is surrounded by the rollers 28 and constitutes a rightward extension of the hub of a gear or pinion 33. The pinion 33 is rotatable on and can move axially of the drive shaft 3. The left-hand end faces of the rollers 29 between the races 31 and 32 of the overrunning clutch 30 abut against a washer 34 which further holds the outer race 31 against axial movement away from the flange 14. The washer 34 is adjacent to a compensating washer 35 and the cylindrical shell 36 of the clutch 30 has two inwardly bent end portions which respectively overlie the right-hand end face of the flange 14 and the left-hand end face of the compensating washer 35. The shell constitutes a means for connecting the pinion 33 and clutch 30 to the shifting sleeve 6. The innermost portion of the compensating washer 35 extends into an external circumferential groove 37 of the pinion 33.

The drive shaft 3 carries a ring-shaped stop 38 which determines the maximum extent of leftward axial movement of the pinion 33 from a first piston shown in FIG. 1. When the pinion 33 abuts against the stop 38 (second position of the pinion), its teeth are in full mesh with the teeth of a torque-receiving gear 40 forming part of the internal combustion engine. A portion of the gear 40 extends into the casing 8 through an arcuate cutout 39 of the extension 7.

The blocking cylinder 20 is provided with a set of external projections have shown as ratchet teeth 41 (see particularly FIG. 2) which are adjacent to the brake disk 27. The casing 8 has a radially extending bore 42 for the cylindrical carrier or shank 43 of a pin-shaped arresting element 44. The extent to which the pin 44 is movable radially outwardly (i.e., away from the adjacent projection or tooth 41 of the blocking cylinder 20) is determined by a split ring 45 which is recessed into a groove machined into the surface surrounding the radial bore 42 of the casing 8. The outer end of the bore 42 is preferably closed by a cap or plug 46.

The shank or carrier 43 has a diametrically extending bore or socket 47 of rectangular cross-sectional outline for the rounded head 48a of one arm 48 of a motiontransmitting bell crank lever 49 which is mounted in the casing 8 on a pivot member 50 extending in parallelism with the drive shaft 3. A torsion spring 51 is provided to bias the bell crank lever 49 clockwise, as viewed in FIG. 2, i.e., so as to move the pin 44 of the arresting means for the blocking cylinder 20 away from the adjacent tooth 41 on the blocking cylinder so that the outer end face of the shank 43 normally abuts against the split ring 45. One leg of the torsion spring 51 is bent around the arm 48'and its other leg reacts against an internal shoulder 52 of the casing 8.

The arm 53 of the bell crank lever 49 consitutes the pivotable armature of an electromagnet 54 having a core 55 which is secured in the casing 8 by one or more screws 56 or analogous fasteners. The winding 57 of the electromagnet 54 surrounds the core 55. One end ofthe winding 57 is conductively connected to a terminal or clamp 59 on the casing 8 by an insulated conductor 58 and the other end of the winding 57 is conductively-connected to the ground (casing 8) by a second insulated conductor 60.

The peripheral surface of the blocking cylinder 20 is formed with an endless groove 61 which extends between the flange 21 and the annulus of projections or teeth 41.

The operation is as follows:

in order to start the internal combustion engine including the gear 40, the driver actuates an operating means here shown as a normally open master switch 62 so that the motor 1 begins to rotate the drive shaft 3. The master switch 62 simultaneously energizes the winding 57 by connecting the terminal 59 to the battery 63 whereby the electromagnet 54 pivots the motion transmitting bell crank lever 49 counterclockwise, as viewed in FIG. 2, so that the arm 48 moves the shank 43 radially inwardly and the pin 44 engages the radial flank of the oncoming tooth 41 on the blocking cylinder 20. The drive shaft 3 rotates the sleeve 6 and blocking cylinder 20 before the pin 44 engagesthe adjacent tooth 41; however, as soon as the pin 44 interrupts the rotation of the blocking cylinder 20, the latter holds the sleeve 6 against further rotation so that the continuously rotating drive shaft 3 causes the sleeve 6 to move axially toward the extension 7 of the casing 8. This is due to the provision of the displacing means including the steep threads 5 on the shaft 3 and complementary internal threads of the sleeve 6. Prior to engagement of the pin 44 with the oncoming tooth 41, the blocking cylinder 20 rotates with the sleeve 6 under the action of the brake spring 17 which urges the coupling member 16 (this member shares the angular movements of the sleeve 6 due to the provision of axially parallel teeth against the brake disk 23 so that the latter bears against the blocking cylinder and urges this cylinder against the brake disk 27 on the flange 14. The brake insures that the sleeve 6 ceases to rotate with the drive shaft 3 as soon as the blocking cylinder 20 is arrested by the pin 44. The brake further constitutes a safety device by permitting the sleeve 6 to rotate relative to the blocking cylinder 20 as soon as the torque which is ap plied to the sleeve 6 exceeds a preselected value at which the spring 17 is incapable of holding the coupling member 16 and brake disk 23 against rotation relative to the blocking cylinder 20. However, as a rule, the sleeve 6 ceases to rotate with the drive shaft 3 as soon as the pin 44 engages one of the teeth 41. Therefore, the rotating drive shaft 3 causes the sleeve 6 to move axially in a direction to the left, as viewed in FIG. 1, and to push the pinion 33 toward the stop 38 through the medium of the overrunning clutch 30 whose inner race 32 is driven by the shaft 3.

If the pinion 33 reaches the gear at the exact moment when some of its teeth register with the tooth spaces of the gear 40, the pinion 33 continues to advance toward and into engagement with the stop 38 and the gear 40 is driven to start the engine. The axial length ofteeth 41 and the position of the pin 44 are selected in such a way that the teeth 41 move beyond the pin 44 when the pinion 33 moves into mesh with the gear 40. Thus, the sleeve 6 is then free to move with the blocking cylinder 20 and clutch 30 along a helical path about he drive shaft 3 until the pinion 33 reaches the stop 38. The pin 44 then extends into the external groove (1] of the blocking cylinder 20 to act as a means for preventing an axial movement of the pinion 33 away from the stop 38, i.e., the pin 44 then insures that the teeth ofthe pinion 33 remain in mesh with the teeth i of the gear 40. The pinion 33 continues to abut against the stop 38 even after the engine is started so that the speed of the pinion 33 then exceeds the speed of the drive shaft 3. The pinion 33 is freeto rotate at such higher speed due to the provision of the overrunning clutch 30.

If the pinion 33 reaches the gear 40 in an angular position in which its teeth are in partial or full alignment with adjacent teeth of the gear 40, the axial movement of the clutch 30 toward the extension 7 is interrupted. The drive shaft 3 then rotates the sleeve 6 relative to the blocking cylinder 20 which is held against rotation by the pin 44. The magnitude of torque which tends to rotate the blocking cylinder 20 while the pin 44 engages one of the teeth 41 is determined by the spring 17, disks 23, 27 and coupling member 16 of the brake. This brake insures that such torque cannot exceed a preselected value. When the sleeve 6 rotates relative to the blocking cylinder 20 (while one or more teeth of the pinion 33 abut against one or more teeth ofthe gear 40), the clutch 30 rotates the pinion 33 until the teeth of the pinion move into alignment with the tooth spaces of the gear 40 so that the pinion 33 can resume its axial movement toward the stop 38. The teeth 41 then moved beyond the pin 44 and the latter enters the groove 61 of the blocking cylinder 20 to maintain the teeth of the pinion 33 in mesh with the teeth of the gear 40 during starting of the engine as well as while the pinion 33 is driven by the gear 40 (as long as the master switch 62 remains closed).

If the teeth of the pinion 33 jam upon contact with the right-hand ends of teeth on the gear 40 (this can happen if the teeth of the pinion 33 and/or gear 40 are worn, chipped or otherwise damaged), the driver simply opens the master switch 62 to arrest the motor 1. The spring 19 is then free to expand and pushes the sleeve 6 toward the armature 4; such movement of the sleeve 6 is shared by the clutch 30 and hence by the pinion 33 which is shifted away from the gear 40. As mentioned above, the spring 19 reacts against the abutment member 10 and bears against the flange 13a of the retainer 13 on the sleeve 6. The movement of the sleeve 6 back to its starting position (pinion 33 spaced apart from the gear 40) involves a rotation of the sleeve due to the provision of steep threads 5 on the shaft 3 which comes to a standstill in response to opening of the master switch 62. Such opening of the master switch 62 results in deenergization of the winding 57 of the electromagnet 54 so that the torsion spring 51 returns the shank 43 into engagement with the split ring 45, Le, the pin 44 is disengaged. from the adjacent tooth 41 on the blocking cylinder 20. Consequently, the blocking cylinder 20 shares the angular movement of the sleeve 6 while the latter moves back to its starting position under the action of the spring 19.

If the drive thereupon again closes the master switch 62, the electromagnet 54 is highly likely to cause the bell crank lever 49 to move the pin 44 into engagement with a different tooth 41 of the blocking cylinder 20. Thus, when the sleeve 6 thereupon moves toward the extension 7, the pinion 33 is likely to move a different group of teeth into engagement with the adjacent teeth of the gear 40 so that the pinion 33 does not jam and the sleeve 6 is free to move the pinion all the way into engagement with the stop 38. In other words, eventual jamming of the pinion 33 in response to contact with the gear 40 merely necessitates an opening and renewed closing of the master switch 62 whereby the pinion is highly likely and practically certain to reach the gear 40 in a different angular position and the starting of the engine can proceed in the aforedescribed manner, either immediately if the teeth of the pinion immediately find the tooth spaces of the gear 40 or with a minor delay if the teeth of the pinion happen to strike the adjacent teeth of the gear 40 end-to-end.

When the engine is started so that the gear 40 rotates the pinion 33 relative to the drive shaft 3, the driver opens the master switch 62 to arrest the motor 1 and to deenergize the winding 57 of the electromagnet 54. The torsion spring 51 causes the bell crank lever 49 to disengage the pin 44 from the adjacent tooth 41 of the blocking cylinder 20 and to move the outer end face of the shank 43 into abutment with the split ring 45. The spring 19 moves the sleeve 6 away from the extension 7 so that the pinion 33 is disengaged from the gear 40. The spring 19 also biases the coupling member 16 against the friction generating lining 18 on the abutment member which insures that the drive shaft 3 of the motor 1 is rapidly decelerated to zero speed.

An advantage of the improved starter is that all parts of the transmission 2 and motor 1 are installed in the housing including the casings 8 and 11, and that neither of these casings must be made larger in order to accommodate the means for shifting the pinion 33 into mesh with the gear 40. Another advantage of the improved starter is its simplicity; as described above, the shifting of pinion 33 toward and into mesh with the gear 40 can begin as soon as the pin 44 engages an oncoming tooth 41 of the blocking cylinder 20 so that the sleeve 6 is compelled to move axially of the drive shaft 3.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitutes essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In a starter for an internal combustion engine having a torque-receiving first gear, a combination comprising a motor having a drive shaft rotatable in a predetermined direction; operating means actuatable to start said motor; a second gear rotatably mounted on and movable axially of said shaft in a first direction from a disengaged first position to a second position of engagement with said first gear and in a second direction back to said first position; a shifting sleeve surrounding said shaft; an overrunning clutch mounted on said shaft and arranged to rotate said second gear in response to rotation of said shaft and to permit said second gear to rotate relative to said shaft in said predetermined direction when said second gear is driven by said first gear at a speed exceeding the speed of said shaft; displacing means having portions provided on said shaft and on said sleeve for moving said sleeve axially in said first direction when said sleeve is held against rotation with said shaft; means for connecting said second gear and said clutch to said sleeve so that said sec- 0nd gear moves toward said second position in response to axial movement of said sleeve in said first direction; and means for holding said sleeve against rotation with said shaft; comprising a blocking member rotatably mounted on said sleeve, arresting means actuatable to interrupt the rotation of said blocking member, and brake means interposed between said blocking member and said sleeve.

2. A combination as defined in claim 1, wherein said displacing means comprises a steep external thread on said shaft and a mating complementary internal thread in said shifting sleeve.

3. A combination as defined in claim 1, wherein said brake means surrounds said shifting sleeve and includes a ring-shaped member movable axially but sharing all angular movements of said sleeve and means for biasing said ring-shaped member against said blocking member.

4. A combination as defined in claim 3, wherein said blocking member comprises at least one external projection and said arresting means comprises an element movable into and from engagement with said projection to thereby respectively prevent and permit rotation of said blocking member with said sleeve, an electromagnet, and motion transmitting means for moving said element into engagement with said projection in response to energization of said electromagnet.

5. A combination as defined in claim 4, wherein said motion transmitting means comprises a lever having a first arm coupled to said element and a second arm constituting the armature of said electromagnet, and means for biasing said lever in a direction to disengage said element from said projection.

6. A combination as defined in claim 1, further comprising a housing for said motor, said second gear, said sleeve, said clutch and said means for holding said sleeve against rotation, abutment means installed in said housing, and means for biasing said sleeve in said second direction to thereby disengage said second gear from said first gear in response to deactivation of said operating means.

7. A combination as defined in claim 6, wherein said means for biasing comprises a spring reacting against said abutment means and bearing against said sleeve, said brake means comprising a ring-shaped member which is movable axially of but shares the angular movements of said sleeve and bears against said abutment means under the action of said biasing means in said first position of said second gear.

8. A combination as defined in claim 6, wherein said sleeve comprises a set of axially parallel external teeth and said brake means comprises a ring-shaped member movable axially on said sleeve and having internal teeth mating with said external teeth, said brake means further comprising a first disk interposed between one end of said blocking member and said ring-shaped member, a second disk interposed between a flange of said sleeve and the other end of said blocking member, and second means for biasing said ring-shaped member and said first disk against said blocking member whereby said blocking member bears against said second disk.

9. A combination as defined in claim 8, further comprising means for non-rotatably connecting said first disk to said blocking member and for non-rotatably connecting said second disk to said flange of said sleeve.

10. A combination as defined in claim 8, further comprising a retainer on said sleeve, said second biasing means comprising a spring reacting against said retainer and bearing against said ring-shaped member.

11. A combination as defined in claim 8, wherein said first disk comprises at least one first projection extending into a recess of said blocking member and said second disk comprises at least one second projection extending into a recess of said flange.

12. A combination as defined in claim 6, wherein said abutment means comprises a friction generating lining and said biasing means urges said ring-shaped member against said lining in said first position of said second gear.

13. A combination as defined in claim 1, wherein said blocking member comprises at least one external projection and a circumferential groove adjacent to said projection, said arresting means comprising an element movable into and from engagement with said projection to thereby respectively prevent and permit rotation of said blocking member and an electromagnet energizable to move said element into engagement with said projection in the first position of said second gear, said element extending into said groove in the second position of said second gear and in the energized condition of said electromagnet.

14. A combination as defined in claim 1, wherein said motor is an electric motor and said operating means comprises a normally open switch which starts said motor in response to closing thereof, and further comprising a housing for said motor, said second gear, said sleeve, said clutch and said means for holding said sleeve against rotation, said arresting means comprising an electromagnet which is installed in said housing and is energizable in response to closing of said switch to thereby prevent rotation of said blocking member.

15. A combination as defined inclaim 1, further comprising a housing for said motor, said sleeve, said second gear, said clutch and said means for holding said sleeve against rotation, said blocking member having an annulus of external teeth and said arresting means comprising an element movable in a bore of said housing substantially radially of said blocking member into and from engagement with one of said teeth to thereby respectively prevent and permit rotation of said blocking member.

16. A combination as defined in claim 15, further comprising means for limiting the extent of movement of said element in said bore in a direction away from said blocking member.

17. A combination as defined in claim 15, wherein said element has a socket and said arresting means further comprises a lever pivotably mounted in said housing and having a first arm extending into said socket and a second arm, and an electromagnet energizable to pivot said lever by way ofsaid second arm in a direction to move said element into engagement with one of said teeth through the medium of said first arm. 

1. In a starter for an internal combustion engine having a torque-receiving first gear, a combination comprising a motor having a drive shaft rotatable in a predetermined direction; operating means actuatable to start said motor; a second gear rotatably mounted on and movable axially of said shaft in a first direction from a disengaged first position to a second position of engagement with said first gear and in a second direction back to said first position; a shifting sleeve surrounding said shaft; an overrunning clutch mounted on said shaft and arranged to rotate said second gear in response to rotation of said shaft and to permit said second gear to rotate relative to said shaft in said predetermined direction when said second gear is driven by said first gear at a speed exceeding the speed of said shaft; displacing means having portions provided on said shaft and on said sleeve for moving said sleeve axially in said first direction when said sleeve is held against rotation with said shaft; means for connecting said second gear and said clutch to said sleeve so that said second gear moves toward said second position in response to axial movement of said sleeve in said first direction; and means for holding said sleeve against rotation with said shaft; comprising a blocking member rotatably mounted on said sleeve, arresting means actuatable to interrupt the rotation of said blocking member, and brake means interposed between said blocking member and said sleeve.
 2. A combination as defined in claim 1, wherein said displacing means comprises a steep external thread on said shaft and a mating complementary internal thread in said shifting sleeve.
 3. A combination as defined in claim 1, wherein said brake means surrounds said shifting sleeve and includes a ring-shaped member movable axially but sharing all angular movements of said sleeve and means for biasing said ring-shaped member against said blocking member.
 4. A combination as defined in claim 3, wherein said blocking member comprises at least one external projection and said arresting means comprises an element movable into and from engagement with said projection to thereby respectively prevent and permit rotation of said blocking member with said sleeve, an electromagnet, and motion transmitting means for moving said element into engagement with said projection in response to energization of said electromagnet.
 5. A combination as defined in claim 4, wherein said motion transmitting means comprises a lever having a first arm coupled to said element and a second arm constituting the armature of said electromagnet, and means for biasing said lever in a direction to disengage said element from said projection.
 6. A combination as defined in claim 1, further comprising a housing for said motor, said second gear, said sleeve, said clutch and saId means for holding said sleeve against rotation, abutment means installed in said housing, and means for biasing said sleeve in said second direction to thereby disengage said second gear from said first gear in response to deactivation of said operating means.
 7. A combination as defined in claim 6, wherein said means for biasing comprises a spring reacting against said abutment means and bearing against said sleeve, said brake means comprising a ring-shaped member which is movable axially of but shares the angular movements of said sleeve and bears against said abutment means under the action of said biasing means in said first position of said second gear.
 8. A combination as defined in claim 6, wherein said sleeve comprises a set of axially parallel external teeth and said brake means comprises a ring-shaped member movable axially on said sleeve and having internal teeth mating with said external teeth, said brake means further comprising a first disk interposed between one end of said blocking member and said ring-shaped member, a second disk interposed between a flange of said sleeve and the other end of said blocking member, and second means for biasing said ring-shaped member and said first disk against said blocking member whereby said blocking member bears against said second disk.
 9. A combination as defined in claim 8, further comprising means for non-rotatably connecting said first disk to said blocking member and for non-rotatably connecting said second disk to said flange of said sleeve.
 10. A combination as defined in claim 8, further comprising a retainer on said sleeve, said second biasing means comprising a spring reacting against said retainer and bearing against said ring-shaped member.
 11. A combination as defined in claim 8, wherein said first disk comprises at least one first projection extending into a recess of said blocking member and said second disk comprises at least one second projection extending into a recess of said flange.
 12. A combination as defined in claim 6, wherein said abutment means comprises a friction generating lining and said biasing means urges said ring-shaped member against said lining in said first position of said second gear.
 13. A combination as defined in claim 1, wherein said blocking member comprises at least one external projection and a circumferential groove adjacent to said projection, said arresting means comprising an element movable into and from engagement with said projection to thereby respectively prevent and permit rotation of said blocking member and an electromagnet energizable to move said element into engagement with said projection in the first position of said second gear, said element extending into said groove in the second position of said second gear and in the energized condition of said electromagnet.
 14. A combination as defined in claim 1, wherein said motor is an electric motor and said operating means comprises a normally open switch which starts said motor in response to closing thereof, and further comprising a housing for said motor, said second gear, said sleeve, said clutch and said means for holding said sleeve against rotation, said arresting means comprising an electromagnet which is installed in said housing and is energizable in response to closing of said switch to thereby prevent rotation of said blocking member.
 15. A combination as defined in claim 1, further comprising a housing for said motor, said sleeve, said second gear, said clutch and said means for holding said sleeve against rotation, said blocking member having an annulus of external teeth and said arresting means comprising an element movable in a bore of said housing substantially radially of said blocking member into and from engagement with one of said teeth to thereby respectively prevent and permit rotation of said blocking member.
 16. A combination as defined in claim 15, further comprising means for limiting the extent of movement of said element in said bore in a Direction away from said blocking member.
 17. A combination as defined in claim 15, wherein said element has a socket and said arresting means further comprises a lever pivotably mounted in said housing and having a first arm extending into said socket and a second arm, and an electromagnet energizable to pivot said lever by way of said second arm in a direction to move said element into engagement with one of said teeth through the medium of said first arm. 